Characterization of polymethoxyflavone demethylation during drying processes of citrus peels

Anti-influenza activity of CPAVM1 protease secreted by Bacillus subtilis LjM2

Bacillus spp. has been considered a promising source for identifying new antimicrobial substances, including anti-viral candidates. Here, we successfully isolated a number of bacteria strains from aged dry citrus peel (Chenpi). Of note, the culture supernatant of a new isolate named Bacillus subtilis LjM2 demonstrated strong inhibition of influenza A virus (IAV) infection in multiple experimental systems in vitro and in vivo. In addition, the anti-viral effect of LjM2 was attributed to its direct lysis of viral particles. Further analysis showed that a protease which we named CPAVM1 isolated from the culture supernatant of LjM2 was the key component responsible for its anti-viral function. Importantly, the therapeutic effect of CPAVM1 was still significant when applied 12 hours after IAV infection of experimental mice. Moreover, we found that the CPAVM1 protease cleaved multiple IAV proteins via targeting basic amino acid Arg or Lys. Furthermore, this study reveals the molecular structure and catalytic mechanism of CPAVM1 protease. During catalysis, Tyr75, Tyr77, and Tyr102 are important active sites. Therefore, the present work identified a special protease CPAVM1 secreted by a new strain of Bacillus subtilis LjM2 against influenza A virus infection via direct cleavage of critical viral proteins, thus facilitates future biotechnological applications of Bacillus subtilis LjM2 and the protease CPAVM1.

Unveiling the Chemistry of Citrus Peel: Insights into Nutraceutical Potential and Therapeutic Applications

The recent millennium has witnessed a notable shift in consumer focus towards natural products for addressing lifestyle-related disorders, driven by their safety and cost-effectiveness. Nutraceuticals and functional foods play an imperative role by meeting nutritional needs and offering medicinal benefits. With increased scientific knowledge and awareness, the significance of a healthy lifestyle, including diet, in reducing disease risk is widely acknowledged, facilitating access to a diverse and safer diet for longevity. Plant-based foods rich in phytochemicals are increasingly popular and effectively utilized in disease management. Agricultural waste from plant-based foods is being recognized as a valuable source of nutraceuticals for dietary interventions. Citrus peels, known for their diverse flavonoids, are emerging as a promising health-promoting ingredient. Globally, citrus production yields approximately 15 million tons of by-products annually, highlighting the substantial potential for utilizing citrus waste in phyto-therapeutic and nutraceutical applications. Citrus peels are a rich source of flavonoids, with concentrations ranging from 2.5 to 5.5 g/100 g dry weight, depending on the citrus variety. The most abundant flavonoids in citrus peel include hesperidin and naringin, as well as essential oils rich in monoterpenes like limonene. The peel extracts exhibit high antioxidant capacity, with DPPH radical scavenging activities ranging from 70 to 90%, comparable to synthetic antioxidants like BHA and BHT. Additionally, the flavonoids present in citrus peel have been found to have antioxidant properties, which can help reduce oxidative stress by 30% and cardiovascular disease by 25%. Potent anti-inflammatory effects have also been demonstrated, reducing inflammatory markers such as IL-6 and TNF-α by up to 40% in cell culture studies. These findings highlight the potential of citrus peel as a valuable source of nutraceuticals in diet-based therapies.

The Browning Properties, Antioxidant Activity, and α-Glucosidase Inhibitory Improvement of Aged Oranges (Citrus sinensis)

Oranges contain many natural active chemicals, organic acids, and polysaccharides. Aging processing is commonly used to modify the color, quality, functional components, and stability of fruits. This study assesses the preparation of aging black oranges using various pre-treatments and solid fermentation. Oranges were aged for six weeks in fresh, non-blanching, blanching, and hot air-assisted aging cycle (AA) groups. The oranges' shrinkage ratio, color difference values, and soluble solids content changed significantly (p < 0.05). Principal component analysis indicated that aging fermentation treatment accelerated glycolysis and increased the ratio of reducing sugars. The enhanced browning can be associated with the oxidation of ascorbic acid (0.66-0.47 mg/g) and the formation of 5-hydroxymethylfurfural (5-HMF) (0.09 mg/g). Furthermore, the presence of free polyphenols led to an increase in the total polyphenol and total flavonoid content. It also had a synergistic effect with 5-HMF in increasing the 2,2-diphenyl-1-picrylhydrazyl free radical-scavenging capacity and ferric ion-reducing antioxidant power (p < 0.05). AA had superior α-glucosidase inhibitory ability increasing from 67.31 to 80.48%. It also reduced the development time by 33%. Therefore, aging technology can enhance the bioactive compounds in oranges and provide a reference for future whole-fruit aging fermentation and health product creation.

Synthetic Studies toward 5,6,7,3',4'-Monomethoxytetrahydroxyflavones: Synthesis of Pedalitin

During the synthetic studies toward 5,6,7,3',4'-monomethoxytetrahydroxyflavones, a concise pedalitin synthesis procedure was achieved. As previously reported, 6-hydroxy-2,3,4-trimethoxyacetophenone was prepared by Friedel-Crafts acylation of 1,4-dihydroxy-2,6-dimethoxybenzene with boron trifluoride diethyl etherate in acetic acid. When aldol condensation of 6-hydroxy-2,3,4-trimethoxyacetophenone 2b with vanillin was performed in basic conditions, it produced 2'-hydroxychalcone 3b, and, surprisingly, along with 3-hydroxyflavone 4 in a considerable amount. We propose that this oxidative cyclization is presumably due to the contribution of a quinone methide, likely to be subjected to aerobic oxidation. The chalcone was then subjected to oxidative cyclization with iodine in dimethyl sulfoxide to afford flavone 5 in good yield. To our delight, serial demethylation of the three methoxy groups at the 5-, 6-, and 3'-positions of 5 proceeded smoothly to produce pedalitin 1, under hydrogen bromide solution (30% in acetic acid). The crystal structures of 3-hydroxyflavone 4 and pedalitin tetraacetate 6 were unambiguously determined by X-ray crystallography.

Citri Reticulatae Pericarpium Limits TLR-4-Triggered Inflammatory Response in Raw264.7 Macrophages by Activating RasGRP3

Inflammation is an important immune response to pathogen invasion, but excessive inflammation leads to tissue injury and even cytokine storm. Therefore, proper response is needed depending on the intensity of the infection. Ras guanine nucleotide releasing protein 3 (RasGRP3) is a regulator of the TLR-mediated response. In low-intensity inflammation, it negatively regulates production of pro-inflammatory cytokines, especially IL-6. Citri Reticulatae Pericarpium, the peel of Citrus reticulata Blanco, is a major medicinal herb in Korean medicine. The present study aims to investigate whether the Citri Reticulatae Pericarpium extract (CRE) has immunomodulatory activity using the Raw264.7 macrophage. Also, we investigated the effect of CRE on RasGRP3 expression. In the present study, CRE reduced IL-6 production in the low-LPS environment (1 ng/mL) and did not in the high-LPS environment (100 ng/mL). The suppression of IL-6 production in the low-LPS environment (1 ng/mL) was abolished after the pretreatment of RasGRP3 siRNA. The reduced RasGRP3 protein content by 100 ng/mL LPS treatment was increased by CRE treatment. Additionally, nobiletin, a major component of CRE showed a suppressive effect on IL-6 production in the low-LPS environment (1 ng/mL). The present results suggest that CRE alleviates inflammatory response via activating RasGRP3 expression in low-intensity inflammation.

Antioxidants from different citrus peels provide protection against cancer

Cancer is one of the leading causes of death. Despite significant advancements in the discovery of medications for the treatment of cancer, these drugs are hindered by applicability and efficacy issues and frequently exhibit major side effects that can further impair patients 'quality of life. Therefore, the development of therapeutically sound anti-cancer medicines derived from natural products has gained prominence in the field of functional foods. Some of these compounds have shown efficacy in the prevention and treatment of cancer as well as low toxicity. Additionally, many recent studies have explored the recycling of agro-industrial waste to create bioactive chemicals. Citrus peels are produced in vast quantities in the food processing sector; due to their abundance of flavonoids, they may be inexpensive sources of protection against several cancers. Citrus is a common type of fruit that contains a variety of nutrients. In particular, the antioxidant chemicals found in citrus peel have been identified as potential cancer-fighting agents. Antioxidant substances such as flavonoids prevent the development of cancer by inhibiting the metastatic cascade, decreasing the mobility of cancer cells in the circulatory system, promoting apoptosis, and suppressing angiogenesis. To explore the most effective uses of citrus peel-derived antioxidants, this review presents background information, an overview of the role of citrus antioxidants in cancer therapy, and a discussion of the key underlying molecular mechanisms.

Review of recent advances on health benefits, microbial transformations, and authenticity identification of Citri reticulatae Pericarpium bioactive compounds

The extensive health-promoting effects of Citri Reticulatae Pericarpium (CRP) have attracted researchers' interest. The difference in storage time, varieties and origin of CRP are closely related to the content of bioactive compounds they contain. The consitituent transformation mediated by environmental microorganisms (bacteria and fungi) and the production of new bioactive components during the storage process may be the main reason for 'the older, the better' of CRP. In addition, the gap in price between different varieties can be as large as 8 times, while the difference due to age can even reach 20 times, making the 'marketing young-CRP as old-CRP and counterfeiting origin' flood the entire market, seriously harming consumers' interests. However, so far, the research on CRP is relatively decentralized. In particular, a summary of the microbial transformation and authenticity identification of CRP has not been reported. Therefore, this review systematically summarized the recent advances on the main bioactive compounds, the major biological activities, the microbial transformation process, the structure, and content changes of the active substances during the transformation process, and authenticity identification of CRP. Furthermore, challenges and perspectives concerning the future research on CRP were proposed.

Polymethoxyflavones from citrus peel: advances in extraction methods, biological properties, and potential applications

Citrus peel, as an effective component of citrus by-products, contains a large number of natural active components, including pectin, vitamins, dietary fiber, essential oil, phenolic compounds, flavonoids, and so on. With the development of the circular economy, citrus peel has attracted extensive concern in the food industry. The exploitation of citrus peel would assist in excavating potential properties and alleviating the environmental burden. Polymethoxyflavones (PMFs) exist almost in citrus peel, which have remarkable biological activities including antioxidant, anti-inflammatory, anti-cancer, and anti-obesity. Therefore, PMFs from citrus peel have the potential to develop as dietary supplements in the near future. Collectively, it is essential to take action to optimize the extraction conditions of PMFs and make the most of the extracts. This review mainly compiles several extraction methods and bioactivities of PMFs from citrus peel and introduces different applications including food processing, pharmaceutical industry, and plant rhizosphere to develop better utilization of citrus PMFs.

Characterization of precipitation from citrus vinegar during ageing: chemical constituents, formation mechanism and anti-proliferative effect

Precipitation formation commonly occurs in the ageing step of fermented citrus vinegar. Hitherto, the chemical characteristics and biological properties of precipitates remain unveiled. This study focused on investigating the chemical profile, formation mechanism and biological repurposing of precipitates. Nine principal components, two flavonoid glycosides and their aglycones along with five polymethoxyflavones (PMFs), were identified from a methanol extract of precipitates. Using hydrolysis models, we demonstrated that insoluble aglycones were generated through the breakage of glycosidic bonds in flavonoid glycosides under acidic condition. Moreover, soluble bound-PMFs were destroyed by yeast-acid hybrid catalysis to release insoluble free-PMFs to form precipitates. A methanol extract of precipitates exhibited a potent anti-proliferative effect on MCF-7 cells (IC₅₀ = 0.032 μg μL^-1) via inhibiting tubulin polymerization. This study will be helpful for the food industry to aid optimizing citrus vinegar brewing and for reutilizing precipitates for functional foods and health products. Furthermore, it also provides a green strategy of PMFs enrichment from citrus using an enzyme-acid hybrid system.

Sinensetin suppresses angiogenesis in liver cancer by targeting the VEGF/VEGFR2/AKT signaling pathway

Sinensetin (SIN) is a polymethoxy flavone primarily present in citrus fruits. This compound has demonstrated anticancer activity. However, the underlying mechanism of its action has not been fully understood. The present study investigated the impact of SIN on angiogenesis in a liver cancer model. In a murine xenograft tumor model, SIN inhibited the growth of HepG2/C3A human liver hepatoma cell-derived tumors and reduced the expression levels of platelet/endothelial cell adhesion molecule-1 and VEGF. In HepG2/C3A cells, SIN repressed VEGF expression by downregulating hypoxia-inducible factor expression. In cultured human umbilical vein endothelial cells, SIN increased apoptosis and repressed migration and tube formation. In addition, SIN decreased the phosphorylation of VEGFR2 and inhibited the AKT signaling pathway. Molecular docking demonstrated that the VEGFR2 core domain effectively combined with SIN at various important residues. Collectively, these data suggested that SIN inhibited liver cancer angiogenesis by regulating VEGF/VEGFR2/AKT signaling.

UHPLC-Q-TOF-MS/MS-based Metabolite Profiling of Ganpu Tea in Rat Urine and Feces

Ganpu tea is a novel type of beverage produced from Pu-erh tea stuffed in the pericarp of Citrus reticulata “Chachi”. It has gained considerable popularity in China owing to its inviting flavor and health effects. However, the in vivo metabolites of Ganpu tea, which may contribute to its overall health effects, are still unclear. In the present work, rat urine and feces samples were collected after oral administration of Ganpu tea extract (GTE), and then subjected to ultra-high-performance liquid chromatography/quadrupole-time-of-flight tandem mass spectrometry (UHPLC-Q-TOF-MS/MS)-based metabolite profiling. As a result, 27 prototype compounds and 41 metabolites derived from caffeic acid, gallic acid, p-coumaric acid, xanthine, catechin, polymethoxyflavone, (PMF) flavanone, and flavone were identified in rat urine and feces. Based on the detected metabolites, the ingested prototype compounds derived from Ganpu tea were found to undergo extensive phase II metabolism in rats, especially and sulfation. These results will be valuable for interpreting the health effects of Ganpu tea.

Bioactive Compounds of Citrus Fruits: A Review of Composition and Health Benefits of Carotenoids, Flavonoids, Limonoids, and Terpenes

The increased consumption of fruits, vegetables, and whole grains contributes to the reduced risk of many diseases related to metabolic syndrome, including neurodegenerative diseases, cardiovascular disease (CVD), diabetes, and cancer. Citrus, the genus Citrus L., is one of the most important fruit crops, rich in carotenoids, flavonoids, terpenes, limonoids, and many other bioactive compounds of nutritional and nutraceutical value. Moreover, polymethoxylated flavones (PMFs), a unique class of bioactive flavonoids, abundantly occur in citrus fruits. In addition, citrus essential oil, rich in limonoids and terpenes, is an economically important product due to its potent antioxidant, antimicrobial, and flavoring properties. Mechanistic, observational, and intervention studies have demonstrated the health benefits of citrus bioactives in minimizing the risk of metabolic syndrome. This review provides a comprehensive view of the composition of carotenoids, flavonoids, terpenes, and limonoids of citrus fruits and their associated health benefits.

Valorization of Taiwan's Citrus depressa Hayata peels as a source of nobiletin and tangeretin using simple ultrasonic-assisted extraction

As the highest yield crop worldwide, citrus peels that possess bioactive compounds were discarded as a futile by-product. Ultrasonication with environmentally friendly solvent (50% ethanol and ddH₂O) were used in the present study to extract flavonoids from Citrus depressa Hayata peels with extraction period and fruit maturity as other variables. DPPH scavenging activity was investigated. Qualitative flavonoid content analysis was done by UV/Vis and FTIR-ATR spectra. Quantification of flavonoid using LC-MS/MS found that solvent type, fruit maturity, and ultrasonication period significantly affect the extracted flavonoid yield (p < 0.05). Extraction using 50% ethanol showed a higher yield than ddH₂O. Flavonoid content was also higher in unripe than ripe samples. Nobiletin, tangeretin, and rutin were dominant among the identified compounds in all sample treatments. Flavonoid content in Citrus depressa Hayata extract was found to negatively correlate to DPPH scavenging activity, which needs further research to identify other bioactivities of these flavonoids.

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Utilization of simple ultrasonication method with less preparation to extract flavonoids from Citrus depressa Hayata peels.

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Fruit maturity, extraction time and solvent preference significantly affect the yield of extracted flavonoid.

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Environmentally friendly solvent for extraction, deliver a comparable yield of flavonoid compounds to other methods.

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The negative correlation of extracted flavonoid to DPPH scavenging activity.

Nutrients and bioactives in citrus fruits: Different citrus varieties, fruit parts, and growth stages

Citrus fruits are consumed in large quantities worldwide due to their attractive aromas and taste, as well as their high nutritional values and various health-promoting effects, which are due to their abundance of nutrients and bioactives. In addition to water, carbohydrates, vitamins, minerals, and dietary fibers are important nutrients in citrus, providing them with high nutritional values. Citrus fruits are also rich in various bioactives such as flavonoids, essential oils, carotenoids, limonoids, and synephrines, which protect from various ailments, including cancer and inflammatory, digestive, and cardiovascular diseases. The composition and content of nutrients and bioactives differ significantly among citrus varieties, fruit parts, and growth stages. To better understand the nutrient and bioactive profiles of citrus fruits and provide guidance for the utilization of high-value citrus resources, this review systematically summarizes the nutrients and bioactives in citrus fruit, including their contents, structural characteristics, and potential health benefits. We also explore the composition variation in different citrus varieties, fruits parts, and growth stages, as well as their health-promoting effects and applications.

Evaluation of dynamic changes in the bioactive components in Citri Reticulatae Pericarpium (Citrus reticulata 'Chachi') under different harvesting and drying conditions

BACKGROUND

The Citrus reticulata 'Chachi' pericarp (CRCP) is one cultivar of Citri Reticulatae Pericarpium (Chenpi), which is widely applied in medicine and food. To determine the potential value of CRCP harvested at different stages and subjected to different drying processes, the dynamic changes in the bioactive components were profiled and evaluated in this study.

RESULTS

The contents of all non-volatile components, i.e. synephrine, limonin, phenolic acids and flavonoids, decreased with delayed harvest time. The volatiles thujene, α-pinene, β-pinene, d-citronellol, d-citronellal, decanal, linalool, geraniol, l-cis-carveol, terpinen-4-ol, α-terpineol, carvacrol, perillaldehyde, methyl 2-(methylamino)benzoate and d-limonene were considered the characteristic components for distinguishing CRCP harvested at different stages. Phenolic acids, synephrine and limonin were stable at different drying temperatures; however, high-temperature drying at 60 °C induced a significant transformation in the flavonoids (especially polymethoxyflavones) and volatile substances in CRCP.

CONCLUSIONS

The results suggested that most of the bioactive components declined with the growth of Citrus reticulata 'Chachi'. And it is believed that the fresh peel should be naturally sun-dried or dried at low temperature (30 or 45 °C) rather than at high temperature (60 °C) to prevent excessive loss of nutrients. © 2020 Society of Chemical Industry.

Sinensetin suppresses influenza a virus-triggered inflammation through inhibition of NF-κB and MAPKs signalings

Background

Human respiratory system infected with influenza A virus (IAV) elicited a robust pro-inflammatory response that resulted in severe illness and even death. Currently, limited immunomodulator is available to counteract IAV-associated pneumonia in the clinic. Sinensetin, a polymethoxylated flavone with five methoxy groups, has been found to possess anti-agiogenesis, anti-inflammatory and anti-diabetic activities. However, the effects of sinensetin on IAV-triggered pro-inflammatory response remain unclear. In the present study, the anti-inflammatory effects and corresponding possible mechanism of sinensetin in IAV-infected A549 cells were subjected to investigations.

Methods

The cytotoxic effects of sinensetin towards A549 cells was detected by MTT and LDH assays. The antiviral activity of sinensetin against influenza A virus was assayed in A549 cells with an engineered replication-competent influenza A virus carrying Gaussia luciferase reporter gene infection. The effect of sinensetin on influenza A virus-triggered inflammatory reaction was determined by qRT-PCR, Luminex assays, ELISA and Western blot.

Results

Our results showed that sinensetin did not exhibit antiviral activity against A/PR/8/34 (H1N1). Meanwhile, sinensetin treatment significantly decreased IAV-induced expression of pro-inflammatory mediators at mRNA and protein levels, including IL-6, TNF-α, IP-10, IL-8 and MCP-1. Additionally, levels of cyclooxygenase (COX)-2 and the downstream product prostaglandin E₂ (PGE₂) up-regulated by IAV infection were dramatically suppressed by sinensetin. The mechanistic investigation revealed that sinensetin treatment suppressed the NF-κB transcriptional activity using the NF-κB reporter stable HEK293 cell line stimulated with TNF-α (20 ng/mL) or influenza H1N1 virus. Furthermore, sinensetin abrogated influenza H1N1 virus-induced activation of NF-κB, ERK1/2 MAPK and p38 MAPK signalings.

Conclusion

Collectively, our results indicated that sinensetin has potential capacity to attenuate IAV-triggered pro-inflammatory response via inactivation of NF-κB, ERK1/2 MAPK and p38 MAPK signalings, which implied that sinensetin may be a promising candidate drug for influenza H1N1 virus infection therapeutics.

Semi-Continuous Subcritical Water Extraction of Flavonoids from Citrus unshiu Peel: Their Antioxidant and Enzyme Inhibitory Activities

We extracted and hydrolyzed bioactive flavonoids from C. unshiu peel using subcritical water (SW) in a semi-continuous mode. The individual flavonoid yields, antioxidant and enzyme inhibitory activities of the SW extracts were analyzed. The extraction yields of hesperidin and narirutin increased with increasing temperature from 145 °C to 165 °C. Hydrothermal hydrolysis products (HHP), such as monoglucosides (hesperetin-7-O-glucoside and prunin) and aglycones (hesperetin and naringenin) were obtained in the SW extracts at temperatures above 160 °C. The sum of hesperidin and its HHP in the SW extracts was strongly correlated with antioxidant activities, whereas the contents of hesperetin and naringenin were strongly correlated with enzyme inhibitory activities. Hesperetin exhibited the highest antioxidant activities (2,2-diphenyl-1-picrylhydrazyl radical scavenging activity, ferric-reducing antioxidant power, and oxygen radical absorbance capacity), whereas hesperetin-7-O-glucoside exhibited the highest enzyme inhibitory activities (angiotensin-І converting enzyme (ACE) and pancreatic lipase (PL)). Naringenin exhibited the highest enzyme inhibitory activities (xanthine oxidase and α-glucosidase). PMFs (sinensetin, nobiletin, and tangeretin) also exhibited relatively high inhibitory activities against ACE and PL. This study confirms the potential of SW for extracting and hydrolyzing bioactive flavonoids from C. unshiu peel using an environmentally friendly solvent (water) and a shorter extraction time.

A rapid protocol to distinguish between Citri Exocarpium Rubrum and Citri Reticulatae Pericarpium based on the characteristic fingerprint and UHPLC-Q-TOF MS methods

Citri Exocarpium Rubrum and Citri Reticulatae Pericarpium were successfully distinguished by the characteristic fingerprint and UHPLC-Q-TOF MS methods.